Heat Shield Member and Single Crystal Pulling Device

ABSTRACT

A heat shielding member  20  that thermally shields the periphery of a single crystal  16  used in a Czochralski single crystal pulling device that pulls the single crystal  16  from a melt  15  that is collected in a crucible  10  is disclosed. The heat shielding member  20  is provided with an approximately cylindrical main body portion  21  arranged so as to surround the single crystal  15 , with a lower end portion thereof extending to the vicinity of the melt  15 , and an approximately annular bottom plate portion  22  that extends in the diameter direction from the bottom end portion of the main body portion  21  to cover the melt. The bottom plate portion  22  is attached to the main body portion  21  in the state of being severed in the circumferential direction at least one location. With this constitution it is possible to provide a heat shielding member with superior durability and a single crystal pulling device that employs the heat shielding member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Czochralski single crystal pullingdevice and to a heat shield member that is used therefor.

2. Description of the Related Art

The Czochralski method is a method conventionally known for growing asingle crystal silicon. The Czochralski method involves melting a rawmaterial in a crucible, immersing a seed crystal in the melt thereof,and then, while rotating the seed crystal and the crucible, slowlypulling the seed crystal up from the melt to make a single crystalsilicon grow thereunder.

The quality of a single crystal that is grown by the Czochralski methodis generally known to be dependent on the temperature during the growingprocess. Radiant heat from the melt in the crucible is given as a factorhaving a major effect on the temperature of the crystal. In order tocontrol it, a heat shielding member made of graphite or the like isnormally placed around the crystal being grown in the Czochralski singlecrystal pulling device (for example, refer to Japanese Unexamined PatentApplication First Publication No. H05-294784 (pages 2 to 4) and JapaneseUnexamined Patent Application First Publication No. H11-290792 (page4)).

Also, in the aforementioned single crystal pulling device, an opticalinstrument is provided for controlling the pull-up speed by measuring ina non-contact way the diameter of the crystal being grown. Therefore, anotch portion (including a slit) is often provided in the heat shieldingmember in order to ensure the visual field.

In the aforementioned single crystal pulling device, the temperature inthe chamber is maintained at not less than 1,000° C. during the pullingup of a single crystal. On the other hand, after completion of thepulling up of a single crystal, the temperature in the chamber isreduced to room temperature, and in this state the single crystal rawmaterial used for the next pulling is supplied to the crucible. That is,an extremely large temperature difference occurs in the chamber betweensupplying of the raw material and pulling up of the single crystal, andthis repeatedly occurs during the manufacturing process of a singlecrystal. Also, a portion, which faces the melt, is provided on thebottom end portion of the above-mentioned heat shielding member. Atemperature difference of 100° C. to 200° C. occurs between the centerportion and the peripheral portion of that portion due to the effects ofinert gas that flows along the surface thereof and the relationshipbetween the arrangement of the crucible and the heater.

For this reason, in the above-mentioned heat shielding member, largestresses may occur during use due to the effects of the aforementionedsevere temperature changes that occur in the chamber and the severetemperature differences that occur in the material, as well as theresidual stress in the material and the thermal expansion differentialbetween a covering material for degradation prevention and the innermaterial or the like. Above all, stress tends to concentrate in thevicinity of a notch portion that is provided for the optical instrument,so that as material quality degradation progresses with repeated use ofthe heat shielding member, there is a possibility of failure occurringduring use. In such a situation, fragments or the like of the heatshielding member would become mixed with the melt in the crucible,rendering the melt unusable, and may become a cause for lowering theyield. In order to avoid this, it is conceivable to replace the heatshielding member before material quality degradation advances. However,since the heat shielding member itself is a comparatively expensivecomponent, frequently replacing it would lead to a cost increase.

The present invention was achieved in view of the aforementionedcircumstances, and has as its object to provide a heat shielding memberwith excellent durability that can relieve thermal stress that occurs inthe material, and a single crystal pulling device that uses the heatshielding member.

SUMMARY OF THE INVENTION

The first aspect of the present invention is, in a Czochralski singlecrystal pulling device that pulls a single crystal from a melt that iscollected in a crucible, a heat shielding member that thermally shieldsthe periphery of the single crystal, which comprises an approximatelycylindrical main body portion arranged so as to surround the singlecrystal, with a lower end portion thereof extending to the vicinity ofthe melt, and an approximately annular bottom plate portion that extendsin the diameter direction from the bottom end portion of the main bodyportion to cover the melt, in which the bottom plate portion is attachedto the main body portion in the state of being severed in thecircumferential direction at least one location.

Here, the approximately cylindrical main body portion includes acylindrical main body portion in which the diameter of both the top andbottom ends thereof are approximately the same dimension, and alsoincludes a main body portion of an inverted truncated cone shape inwhich the diameter gradually narrows from the top end to the bottom end.

The approximately annular bottom plate portion includes a level bottomplate portion in which the heights of the inner circumference and theouter circumference are the same, and also includes an inclined bottomplate portion in which the inner circumference is positioned above orbelow the outer circumference.

A method of attaching the bottom plate portion to the main body portionincludes, for example, providing a support portion that extends to theinner circumference side at the bottom end of the main body portion andattaching the bottom plate portion with the periphery of the bottomplate portion being placed on the upper side of the support portion.

According to the first aspect of the present invention, since theapproximately annular bottom plate portion that covers the melt isattached to the main body portion in the state of being severed in thecircumferential direction at least one location, it is possible torelieve thermal stress generated in the bottom plate portion and preventthermal stress from concentrating in a particular portion of the heatshielding member. That is, in the case of the bottom plate portion beingprovided in a state of being continuous in the circumferential direction(i.e., without severed locations), free thermal expansion of the bottomplate portion is restricted, thereby leading to the possibility of largethermal stress being generated during use. According to the presentinvention, by severing the bottom plate portion in the circumferentialdirection at least one location, it is possible to prevent thegeneration of the aforementioned large thermal stress. As a result, evenif material quality degradation progresses, failure of the heatshielding member is hindered, and so it is possible to increase thedurability of the heat shielding member. Also, since failure of the heatshielding member is hindered, the material cost can be reduced.

The second aspect of the present invention is characterized by a notchportion being provided at the bottom plate portion of the heat shieldingmember according to the first aspect of the present invention and thebottom plate portion being severed along a line that passes through thenotch portion.

Here, the notch portion includes a notch portion that is formed so as tonotch a portion of the inner circumference or the outer circumference ofthe bottom plate portion as well as an opening portion that is formedbetween the inner circumference and the outer circumference. Also, thenotch portion is one not limited to a notch portion that is formed forsecuring the visual field of an optical instrument, but may be a notchportion that is formed for another use.

According to the second aspect of the present invention, since thebottom plate portion is severed along a line that passes through thenotch portion, it is possible to prevent thermal stress fromconcentrating around the notch portion and possible to further improvethe durability of the heat shielding member.

The third aspect of the present invention is a Czochralski singlecrystal pulling device that pulls a single crystal from a melt that iscollected in a crucible, characterized by using the heat shieldingmember according to first or second aspect of the present invention as aheat shielding member that surrounds the periphery of the singlecrystal.

According to the third aspect of the present invention, since the heatshielding member according to first or second aspect of the presentinvention is used as a heat shielding member that surrounds theperiphery of the single crystal, the durability of the heat shieldingmember improves beyond conventional durability, and a reduction in thecost of manufacturing a single crystal can be achieved. Also, it ispossible to reduce the occurrence of such a problem as failure of theheat shielding member during use, and thereby possible to improve theyield.

As described above, the present invention can relieve thermal stressgenerated in the bottom plate portion and prevent thermal stress fromconcentrating in a particular location of the heat shielding member.Accordingly, it is possible to improve the durability of the heatshielding member and reduce the costs of manufacturing a single crystal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing one embodiment of the single crystalpulling device according to the present invention.

FIG. 2 is a perspective view showing the heat shielding member of FIG.1.

FIG. 3A is a plan view showing the bottom plate portion of the heatshielding member of FIG. 1.

FIG. 3B is a plan view showing the bottom plate portion of the heatshielding member of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 3B show one embodiment of a heat shielding member and asingle crystal pulling device employing the heat shielding memberaccording to the present invention. In the drawings, reference number 10denotes a crucible. This crucible 10 consists of an inner layercontainer made from quartz and an outer layer container made fromgraphite and, as shown in FIG. 1, is accommodated in a chamber 11 in astate of being supported by a support shaft 12 in a rotatable andelevatable manner. A heater 13 is disposed around the crucible 10,following the outer circumference thereof, and a pull-up shaft 14, whichis rotatable and elevatable, is provided above the crucible 10 in theopposite direction of the support axis 12. A seed crystal (notillustrated) is attached to the bottom end portion of the pull-up shaft14. By immersing the seed crystal in a melt 15 inside the crucible 10and then slowly pulling the seed crystal up from the melt 15 whilemaking the pull-up shaft 14 and the support shaft 12 rotate in oppositedirections, a single crystal silicon 16 grows at the bottom thereof.

Also, an optical instrument (not illustrated) for measuring the diameterof the aforementioned single crystal 16 being grown is provided at apredetermined position in the chamber 11. The pull-up speed or the likeof the seed crystal is controlled based on the measurement value of thisoptical instrument.

As shown in FIG. 1, a heat shielding member 20 that thermally shieldsthe periphery of the aforementioned single crystal 16 being grown isprovided above the crucible 10. This heat shielding member 20 includesan approximately cylindrical main body portion 21 that is arranged so asto surround the single crystal 16, with a lower end portion thereofextending to the vicinity of the melt 15 in the crucible 10, and anapproximately annular bottom plate portion 22 that is disposed at thebottom end portion of the main body portion 21 in the state of facingthe melt 15. The main body portion 21 and the bottom plate portion 22are both made of graphite or carbon-carbon composite materials or thelike and the surfaces thereof are coated with silicon carbide (SiC).

As shown in FIGS. 1 and 2, a flange portion 23 for making the heatshielding member 20 engage with a frame 17 in the chamber 11 is providedat the top end portion of the main body portion 21. A support portion 24which supports the peripheral edge portion of the bottom plate portion22 is provided at the bottom end portion of the main body portion 21 inthe state of extending to the inner circumference side of the main bodyportion 21.

In the center of the bottom plate portion 22, an opening portion 26 forallowing the aforementioned single crystal 16 to pass therethrough isprovided. As shown in FIG. 2 and FIGS. 3A and 3B, on the innercircumference of the bottom plate portion 22, a notch portion 25 forsecuring the visual field of the optical instrument is formed. Theaforementioned bottom plate portion 22 is attached to the main bodyportion 21 in the state of being severed in the circumferentialdirection along a line that passes through the notch portion 25 to beplurally divided (here, in a state of being divided in half along adiameter L that passes through the notch portion 25).

In the case of growing the single crystal silicon 16 using the singlecrystal pulling device having the aforedescribed constitution, first,polycrystalline silicon, which is the raw material, is supplied to thecrucible 10, and then, after vacuum evacuation of the chamber 11, theheater 13 is activated in the state of introducing an inert gas to flowtherein and the raw material in the crucible 10 is melted. Next, theseed crystal attached to the bottom end portion of the pull-up shaft 14is immersed in the melt 15 in the crucible 10, and from this state thepull-up shaft 14 is raised while making the pull-up shaft 14 and thesupport shaft 12 rotate in opposite directions. Thereby, the singlecrystal silicon 16 is grown under the seed crystal.

In this case, since the periphery of the single crystal silicon 16 issurrounded by the heat shielding member 20, the radiant heat or the likeemitted from the melt 15 in the crucible 10 is blocked by the heatshielding member 20. Accordingly, by preventing a rise in temperature ofthe single crystal 16, the single crystal 16 can be readily controlledto a temperature set in advance, and fluctuations in quality stemmingfrom temperature control of the single crystal 16 can be reduced.

Moreover, according to the heat shielding member 20 of the presentembodiment, since the annular bottom plate portion 22 that faces themelt 15 is attached to the main body portion 21 in the state of beingsevered in the circumferential direction at a plurality of locations,thermal stress generated in the bottom plate portion 22 can be relieved.In particular, in this embodiment, since the bottom plate portion 22 isdivided along a line (diameter L) that passes through the notch portion25, thermal stress can be prevented from concentrating on the perimeterof the notch portion 25. Accordingly, it is possible to improve thedurability of the heat shielding member 20 and hinder failure of theheat shielding member 20 even when material quality degradation hasadvanced.

As a result, it is possible to reduce the occurrence of such a problemas failure of the heat shielding member 20 during use, and therebypossible to improve the yield.

Moreover, in this embodiment, since the bottom plate portion 22 isdivided into two by the diameter L passing through the notch portion 25as a dividing line, split pieces 22 a and 22 b thereof can each be heldin a stable state so as not to fall from the main body portion 21.

In this embodiment, the annular bottom plate portion 22 was divided intotwo by severing the bottom plate portion 22 at two locations, but thepresent invention is not limited thereto. For example, it is possible toadopt a constitution that severs the bottom plate portion 22 at three ormore locations so as to divide the bottom plate portion 22 into three ormore pieces, or a constitution that severs the bottom plate portion 22at only one location so as not to plurally divide the bottom plateportion 22.

As described above, the present invention can relieve thermal stressgenerated in the bottom plate portion and prevent thermal stress fromconcentrating in a particular portion of the heat shielding member.Accordingly, it is possible to improve the durability of the heatshielding member and reduce the costs of manufacturing a single crystal.

1. A heat shielding member, which thermally shields the periphery of asingle crystal, which is used in a Czochralski single crystal pullingdevice that pulls the single crystal from a melt that is collected in acrucible, comprising: an approximately cylindrical main body portionarranged so as to surround the single crystal, with a lower end portionthereof extending to the vicinity of the melt; and an approximatelyannular bottom plate portion that extends in the diameter direction fromthe bottom end portion of the main body portion to cover the melt,wherein the bottom plate portion is attached to the main body portion inthe state of being severed in the circumferential direction at least onelocation.
 2. The heat shielding member according to claim 1, wherein thebottom plate portion further comprises a notch portion, and the bottomplate portion is severed along a line that passes through the notchportion.
 3. A Czochralski single crystal pulling device that pulls asingle crystal from a melt that is collected in a crucible, in which theheat shielding member according to claim 1 or claim 2 is employed as aheat shielding member that surrounds the periphery of the singlecrystal.